1. Field
The present disclosure relates generally to aircraft and, in particular, to managing the flight of an aircraft. Still more particularly, the present disclosure relates to a method and apparatus for identifying a condition at which an aircraft may potentially stall given a current state of the aircraft during flight.
2. Background
The state of an aircraft during flight is determined by a number of factors. These factors may include, for example, without limitation, the speed of the aircraft, the size of the aircraft, the shape of the aircraft, the shape of the wings of the aircraft, the angle of attack of the aircraft, and other types of factors. In some cases, the maneuvering capabilities of the aircraft may change in response to changes in the state of the aircraft during flight.
For example, an aircraft may stall if the angle of attack of the aircraft increases in a manner that causes an amount of lift generated by the aircraft during flight to decrease. As used herein, “lift” is the force generated when air flows over an aircraft during flight. This force directly opposes the weight of the aircraft and holds the aircraft in air.
The particular angle of attack at which the lift generated by the aircraft decreases may vary for different types of aircraft. The angle of attack at which an aircraft can potentially stall may be based on factors such as, for example, without limitation, the profile of the wings of the aircraft, the planform of the wings, the aspect ratio of the wings, and other factors. Further, the angle of attack at which an aircraft can potentially stall corresponds to a particular speed for the aircraft. This speed may be referred to as a “stall speed”.
Some currently available commercial aircraft use an alert system that generates an alert when the speed of the aircraft falls below an alert speed, which is greater than the stall speed by some selected amount. This alert speed may also be referred to as a “minimum speed”. In particular, when the speed of the aircraft is less than the alert speed, an alert is generated such that an operator of the aircraft may take action to prevent or at least reduce the possibility of the aircraft stalling.
The stall speed of an aircraft may determine the maneuvering capabilities of the aircraft. For example, the stall speed may determine the minimum distances required for takeoff and landing by the aircraft. These distances are referred to as the takeoff distance and landing distance, respectively, for the aircraft. The takeoff distance and landing distance for an aircraft are determined by the slowest speeds at which the aircraft is capable of flying during takeoff and landing without stalling. The takeoff and landing speeds for an aircraft may be required to be greater than or equal to the alert speed of the aircraft.
Consequently, the stall speed of an aircraft may affect the maneuvering capabilities of the aircraft at different airports. In particular, the length of a runway from which the aircraft takes off at an airport may need to be at least the length of the takeoff distance. Similarly, the length of the runway onto which the aircraft lands at an airport may need to be at least the length of the landing distance. The takeoff distance and landing distance for an aircraft may be reduced by decreasing the alert speed during takeoff and landing, respectively.
Additionally, the stall speed of an aircraft may affect the ability of the aircraft to maneuver at elevated bank angles with respect to different load factors. For example, the turn radius of the aircraft may be determined by the speed of the aircraft and the maximum bank angle at which the aircraft can fly while staying at, and/or above, the alert speed. In particular, the minimum maneuvering speed at which the aircraft can fly with respect to a selected load factor for the aircraft is required to be greater than the alert speed at the selected load factor.
The takeoff distance and landing distance for an aircraft may be set by various regulations, such as those defined by the Federal Aviation Administration. Some currently used alert systems are conservative with respect to alert speed. For example, with these types of alert systems, alerts may be generated at higher alert speeds to increase safety in operating the aircraft. However, these higher alert speeds may cause some aircraft to be unable to operate at some airports. Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above as well as possibly other issues.